The invention relates to a seal for use with a rotor apparatus. In particular, the invention relates to a dynamic seal that prevents foreign material from entering an air bearing for a cutting tool mounted on a rotor apparatus. In operation, the dynamic seal adds essentially no friction to the surface of the rotor carrying the cutting tool.
Air bearings are widely used with rotor-mounted cutting tools in drilling grinding, and routing applications. Air bearings have been found to possess advantages over ball bearings in certain applications. The operating life of ball bearings, for example, substantially decreases when rotational speeds of the rotor exceed approximately 60,000 revolutions per minute. Air bearings are therefore frequently substituted for ball bearings in such high speed applications.
Air bearings operate at varying pressures and in varying configurations. Typically, the air bearing operates by directing air into the bearing space along the surface of the rotor toward the cutting tool and through and air exhaust gap. The air exhaust gap is small, usually on the order of approximately 0.0002 inches.
It has been previously thought by tool designers in this field that the air exhaust flowing toward the cutting tool would prevent fragmentary scraps and debris ejected from the workpiece from entering the air bearing during the cutting operation. Tests have shown, however, that such debris in fact accumulates on the rotor surface and in the air bearing space, probably because of turbulence and eddy currents in the vicinity of the air exhaust gap. Such accumulation of debris greatly reduces the life of the air bearing and rotor, since the rotor is subject to sticking and requires constant cleaning to operate smoothly. Eventually, the rotor will freeze or seize up from the accumulation of debris.